In primary hypothyroidism, which pattern best matches TSH, FT4, TT3/TT4, and T3 uptake?

• A. TSH high; FT4 low; TT3/TT4 low; T3 uptake low
• B. TSH low; FT4 high; TT3/TT4 high; T3 uptake high
• C. TSH high; FT4 high; TT3/TT4 low; T3 uptake low
• D. TSH normal; FT4 normal; TT3/TT4 normal; T3 uptake normal

Answer: (A)

When the thyroid gland isn’t producing enough hormone (primary hypothyroidism), the pituitary responds by increasing TSH to try to stimulate the thyroid. This loss of negative feedback causes free T4 to fall. With less thyroid hormone circulating, total T3 and total T4 also decrease. The T3 uptake test, as used in older thyroid profiles, tracks the availability of circulating thyroid hormone; with low free hormone, the uptake value tends to be reduced. So the pattern you’d expect is higher TSH, lower FT4, lower TT3/TT4, and a lower T3 uptake.